The exterior of the mitrailleuse has the appearance of a bronze cannon. This case encloses 25 rifled tubes brazed together. The rear part of the cannon presents a vertical cavity, very large and nearly rectangular in shape. This cavity is called the cage, and is intended to receive the breech-block and firing mechanism. The breech-block is a cubical block containing prolongations of the 25 barrels which serve as chambers for the cartridges. When loaded, this block drops into the forward part of the cage. The lock mechanism is a box containing 25 firing-pins, arranged with guides and springs on the ordinary system. This box is movable longitudinally by the motion of a breech-screw, which also sets up the breech-block when in place. The motion forward of this box retracts the firing-pins, which are then held until released in rapid succession by a turn of the crank. After firing, the breech-screw is backed, the block taken out and a loaded one is put in its place, the screw is set up retracting the locks, and the piece is ready for firing again. _Hotchkiss Machine-Gun._ (See United States Ordnance.) This gun is an American invention, but was first introduced into the French Navy. CARRIAGES. Gun-carriages in the French Navy are classified as follows: Slide-carriages for heavy broadside-guns. Turret-carriages and revolving-slide carriages for heavy guns. Directing-bar carriages for broadside-guns. Four-truck and rear-chock carriages for broadside-guns. Gun-boat carriages for bronze guns. Boat-carriages for bronze guns. Mountain carriages for bronze guns. Mitrailleuse saddle or fork for machine-guns. _Slide-Carriage for 27-cm. and 24-cm. Guns._ [Illustration: Elevating-Gear and Compressor, 24-cm. Gun.]